Directive aerial



M. H. BODMER ETAL 2,940,078

DIRECTIVE AERIAL June 7, 1960 Filed July 25, 1957 3 Sheets-Sheet 1 'ay www rroHA/Ers June "7', v,1960 M. H. BoDMr-:R ErAL 2,940,078

DIRECTIVE AERIAL Filed July 25, 1957 3 Sheets-Sheet 2 L 201. Fig- 2 By HM awf/ HrramvE/s 9ill'nited States ljatent 0" DIRECTIVE AERIAL Hubert Bodmer and Cornelis Augustinus van Staaden, both of Hengelo, Netherlands, assgnors to NN. Hollandse Signaalapparaten, Hengelo, Netherl lands, a Dutch corporation Filed July 25, 1957, Ser. No. 674,094 Y Claims priority, application Great Britain Aug. 7, 1956 8 Claims. (Cl. 343-761) This invention relates to a radar aerial the beam of which is capable of performing at choice various types of scanning motions. n modern radar apparatus the exact measurement of the target coordinates is, as a rule, eifected by means of a conically scanning beam. Such a beam provides highly accurate values of the target coordinates, but is unsuitable for searching for a target. It is therefore dirable that the apparatus should also be able to produce a beam which performs a scanning motion which is more suitable for searching. In certain radar systems this is achieved by causing the completeV aerial reiiector to oscillate around an elevation axis whilst the aerial system is caused to ezect a searching motion around the training axis. In such a system the moment of inertia of the aerial reflector sets a limit to the scanning frequency during searching, and, consequently, also to the searching velocity. In other radar systems the radiator Iwhich irradiates the aerial reflector is capable of performing various types of scanning motions, causing,7 the beam to effect either a conically scanning motion or a spiral or a linear scanning motion. Such an aerial requires a complicated scanning system which limits the scanning frequency of all scanning motions, especially of the conical scanning motion. The limitation of this frequency is -in many cases unacceptable as it causes the measurement of the coordinates of targets moving at high speed to be less accurate. A radar system which meets high technical requirements is described in the British application for patent Nr. 5746/54 and possesses an aerial for linear scanning as Well as a separate aerial for conical scanning, these aerials being coupled so as to perform corresponding motions around parallel or coinciding searching axes whilst a special comparison system permits the aerial for conical scanning to be aimed around a second anis in accordance with the measuring results obtained by the aerial for linear scanning. This system permits the beam concentrating devices as well as the scanning mechanisms of the aerials to be completely adapted to the requirements of the scanning motions to be performed by the beam produced by the aerials. The system is, however, expensive, because it requires two separate systems for concentrating the beams, such as aerial reectors;

According to the present invention a directive radar aerial, producing a beam which is capable of performing at choice various types of scanning motion, is provided with a beam concentrating device and an eccentrically rotatable wave guide nozzle as well as with a second radiating system which is situated in the space between the eccentrically rotatable wave guide nozzle and the beam concentrating device and is capable of performing at least one type of scanning motion, this radiating system consisting of at least one radiating doublet cooperating with an auxiliary reiiecting system which causes a substantial part of that radiation of the second radiating system which otherwise would not reach the beam concentrating device to be reected in the direction of this device.

When using the new aerial according to the invention',

andere Patented June 7, 1960 coordinate measurement is eected by means of the conically scanning beam which isr generated by means of the eccentricallyY rotatable wave guide nozzle, whilst the second radiator is in such a position that it will not seriously hamper the production of the conically scanning beam. During searching, the second radiator is active, and performs such motions as are necessary to cause the desired scanning motions of the searching beam, whilst the complete aerial reflector performs a searching motion. The scanning motion performed by the second radiator may be a spiral scanning motion or a linear scanning motion, for instance. The linear scanning motion of the second radiator may in some cases be combined with an auxiliary scanning motion in a second direction as will be described below. Preferably the second radiator is supported by the wave guide or by a coaxial line by which it is fed. The radiating system consists of a single doublet, or, if it is necessary to reduce the width of the beam by which the second radiator irradiates the reectorso as to adapt this Width to the dimensions of the reflector, of a system of parallel doublets. In one form of the invention the auxiliary reiiccting system consists of a metal reflector, such as a at piece of sheet metal or a at piece of metal gauze. In other embodiments it consists of a reector doublet or a system of reflector doublets.

vFor the correct operation of the aerial it is essential that the point from which the radiation of the eccentrically during its Vscanning motion the point' from which the radiation of the second radiator appears to emanate should be able, during theperforming of the scanning motion, to pass through the focal point of the device concentrating the beam. One would suppose that it would be impossible to full these conditions sirmiltaneouslyv and that the system consisting of the second radiator and the auxiliary reflector would not be capable of passing in front of the eccentrically rotatable Wave guide mechan ism if both radiators were situated in such a position as to satisfy the above conditions. The inventor has shown, however, that when the said conditions are fuliilled there is still space left between the eccentrically rotatable nozzle mechanism and the said second radiating system, permitting the latter system to pass in front of the nozzle mechanism without Vit being necessary to take special measures, such as shifting the rotatable nozzle mechanism backwards.

The doublet or doublets forming part of the second radiating system can be fed either by a wave guide or by a coaxial line system.

When the radiator for conical scanning is operative its radiation should not be impeded by the presence more or less in front of it, of the inner radiator and more especially of the auxiliary reflector of this inner radiator. The second radiator, therefore, should be moved away from the nozzle for conical scanning when this nozzle is to become operative, and preferably locked in a position, in which it permits the passage of the radiation from the said radiator for conical scanning. In an embodiment according to the invention the inner radiator is for this purpose moved by its driving mechanism to an extreme position in its scanning path, and locked in this position.

The presence of the second radiator within the fiel-:i of the eccentrically rotatable nozzle will nevertheless result in the origination of side-lobes of the conically scanning beam. These side-lobes do not necessarily prevent the exact measurement of the target coordinates and for many purposes the aerial described above is perfectly suitable. Side-lobes, however, will in any case reducel the gain of the aerial and although, as a rule, highgain is only required during the searching operation, whilst the.

auxiliary scanning motion will be twice the fundamental frequency of the main scanning motion. If it is necessary for the inner radiator to be able to cause such an auxiliary scanning motion it must vbe supported in a gimbal ring or the like and its` driving system must be able to cause oscillating motions of the radiator in both scanning directions. A simple example of a driving system capable of producing such an auxiliary scanning motion is shown in Fig. 9, in which the wave guide 901 carrying the inner radiator is capable of swinging around an axis 902 supported in the girnbal ring 903, which is itself capable of rotating around the axis 904. The gimbal ring carries alever 905 which is caused to scillate by means of a cam which is not shown` in the iigure, and on which a roller 906, mounted at the extremity of the lever 905, is causedto rest as a result of the tension of a spring acting on the lever 905. Consequently the gimbal ring oscillates around the axis 904 and the wave guide 901 partakes in this oscillating motion as a result of which the radiator performs an auxiliary scanning motion. The main scanning motion is performed around the axis 902, and is caused by a rotating crank 909 which is coupled to the lever 907 of the wave guide 901 by means of a connecting rod 908. As the connecting rod must not impede the auxiliary scanning motion, both ends of the connecting rod 908 are constructed so as to be able to rotate around two mutually perpendicular axes as shown in the gure.

In every case in which it is necessary for a wave guide feeding the inner radiator to be able to swing around an axis, it is coupled to a xed feeding wave guide by means of one of the well known types of rotatable joints. If such a wave guide is supported on a gimbal ring and must be able to perform rotations around two axes, the gimbal support is combined with a universal wave guide joint provided with suitable chokes. If the inner radiator is fed by a coaxial line, then the moving part of the coaxial line is connected by a Well known suitable connecting means to a xed coaxial line.

Fig. 7 shows a retractable movable wave guide feeding the inner radiator. The inner radiator, consisting of the doublet 704 and the small reector 705, is not, however, carried by this wave guide itself but by another wave guide 702, the cross section of which is just a little larger than that of the wave guide 701, and which can be shifted over the wave guide 701. When the apparatus is at rest the outer wave `guide 702 is retained in its retracted position by two cylindrical springs 706. When it is necessary for the inner radiator to become operative it is shifted outwards, for which purpose it is provided with a piston 708 which tits narrowly in the pressure cylinder 707. Compressed gas can be brought into the cylinder 707 through a exible tube 709, causing the piston 708 and the wave guide 702 to be shifted outwards until the piston rests against the right hand end of the cylinder. The wave guides are closed by blocks of low loss dielectric material, such as 703, or by closed diaphragms so that the compressed gas cannot leak away through the wave guides.

lf the polarisation directions of the radiation produced by the two radiators are mutually perpendicular, the parabolic reector must be able to reflect wave energy of both polarisation directions. For this purpose it must consist of two sets of conductors having different directions. ln some cases it may be desirable for the boundaries of the part of the parabolic surface which reiects the wave energy of the one radiator to be different from `the boundaries of the part of the parabolic surface which reects the wave energy of the other radiator. The conically scanning beam, for instance, should preferably be a rotationally symmetric pencil beam so that it is desirable that the part of the parabolic surface concentrating the conically scanning beam should possess a suitable boundary for producing such a rotationally symmetric beam. On the other hand a at beaver tail beam is preferable for searching, and in order to generate such a beam the reflecting parabolic surface should be large in the direction perpendicular to the largest dimension of the beaver tail beam and small in the direction of the largest dimension of the beaver tail beam. If a common reflector is applied for generating the conically scanning beam as well as the linearly scanning beam, it is, as a rule, impossible to adapt the boundaries of the parabolic reecting surface to the shape of beam to be produced. If in this case, however, the polarisation directions of the two beams are mutually perpendicular, an adaptation of the boundaries of the reiiecting surface is stillpossible. For this purpose the reflecting surface consists of two overlapping parts, one of which consists of conductors the direction of which corresponds to the direction of the electrical vector of the radiation of one radiator, whilst the other consists of conductors the direction of which corresponds to the direction of the electrical vector of the radiation produced by the other radiator. An example of such an aerial according to the invention suitable for the production of a linearly scanning beaver tail beam and a conically scanning pencil beam is shown in Fig. yl0.

The Figures 3, 4, 5, and 6 show other examples of radiating systems suitable to be used as the inner radiating system of an aerial according to the invention. In Fig. 4, instead of one radiating doublet, two radiating doublets are applied for the purpose of restricting the width of the beam of wave energy radiated by the radiating system. ASuch a system of doublets is specially important if a fiat beam is to be produced. Fig. 3 shows a radiating system in which, instead of an auxiliary reflector, a reflector doublet is applied. It is obvious that instead of one radiating doublet and one reector, doublet systems consisting of more than one doublet may also be used. Fig. 5 shows a radiator system in which one radiating doublet S01 is fed by a coaxial line 502. As may be seen in the figure, the lower half of the radiating doublet is connected to the outer conductor of the coaxial line, whilst the upper half of the doublet passes through an opening 503 in the outer conductor and is connected to the inner conductor of the feeding coaxial line. In this radiator the circular piece of sheet metal is the auxiliary reflecting system 504. ln the system shown in Fig. 6 this piece of sheet metal is replaced by a reflector doublet 601 in order to reflect the wave guide energy emanating from the doublet which is fed by a coaxial line 602.

What we claim is:

1. A directive antenna array for selectively performing several different scanning motions, said array comprising, in combination, a parabolic main reflector, an outer radiating system facing the reliector to direct a pencil beam upon the same, and an inner radiating system situated between the outer system and the reflector for directing a beaver tail beam upon said reflector, said outer system including a drive motor having a hollow shaft, a wave guide housed within said shaft for rotation in unison therewith and a wave guide nozzle at the wave guide end facing the reector and extending eccenu'ically relative to the rotational axis of the shaft motor, said outer system being mounted in a position in which said guide nozzle rotates in a plane including the focal point of the reector, and said inner system including at least one radiating doublet and an auxiliary reflector positioned to direct radiation emanating from said doublet upon the main reflector.

2. An antenna array according to claim l wherein said doublet is disposed between the nozzle opening and the auxiliary reliector.

3. An antenna array according `to claim l and comprising a moving means for imparting a reciprocatory scanning motion to the doublet and the auxiliary reector of said inner system, and locking means for releasably 7. locking the doublet and the auxiliary reector 'in one of the limit'positioris of the `scanning mot-ion... I 24; 'An'antennaiar'ray according to claim 3j and com-prisirig retraction,means` for selectively retracting said doublet Y and'said auxiliary reector into a position beyond said limit position of the scanning motion of the inner system.

5. YAn antenna array i according to claim 4 wherein said movingl rneansjcomprises linkage meansy including Several pivotally hinged linka, and wherein said retraction means comprises means for spatially'fdisplacing the. pivot YYpoints of one'of` said; links so as Vto eiectY sadretraction benve'en s aidlimitposition. v i v An antenna array according.Y to claim :1..wherein said nozzle and-said inner radiating system arel disposed f Y in -a relati,o nslnipY such that therpolarization directions of the radiation emanating from `the nozzle 'andrtheinner Y system respectively are at Vright'angles whereby the main' reilector rreiects` the `Wave Venergyof bothk polarization directions. v 1 Y 7. An antenna array according to claim 6 wherein said main reflector comprises two portions overlapping each other,Y said portions including conducting elements having a direction parallel to the direction of the electrical 8T4 vector of the radiation fed to said main reector by one ofthe systems, and the other including conducting ele'- ments-having `adirecition Yparallel to the direction'of the electrical vector ofi'radiation fed tothe main reilector from the other system. Y g I 1- V 8.Y An antenna Varray according to claim 1 wherein said Y radiating doublet vand said auxiliary .reector are mounted onawave guideY axially slidable relative to said nozzle Y of said 'inner radiating system for controlling the spacing therebetween.' p j Y Y 1 References Cited .in thecileof Vpatent UNITED STATES'PATENTS V ...rw my w 

